1. Field of the Invention
The present invention relates to a radio receiving device suitable for mobile communication and, more particularly, to a radio receiving device which can be used in either or both of a base station and a mobile station to measure electric field level of a receiving channel and adjacent channels.
2. Description of the Prior Art
For example, in a radio receiving device for mobile communication, in order to evaluate the quality of communication, the electric field levels of a receiving channel and adjacent channels of higher- and lower-frequencies are measured. For example, in a base station for a mobile communication system, in order to evaluate the quality of communication between the base station and a given mobile station, the electric field levels of a radio wave transmitted from the mobile station on the receiving channel and the adjacent channels of higher- and lower-frequencies are measured. The same operation may be performed in a mobile station in the mobile communication system.
FIG. 1 is a block diagram showing a conventional radio receiving device disclosed in Japanese Unexamined Patent Publication No. SHO 61-256839. FIG. 2 shows the characteristics of a band-pass filter designed to filter a wave transmitted through a receiving channel in the device.
This radio receiving device includes a frequency converter 2 for converting the frequency of a received signal into a lower-frequency, i.e., an IF (intermediate frequency), a band-pass filter 32a for filtering only a signal on a receiving channel to be demodulated, and band-pass filters 32b and 32c for filtering only signals on adjacent channels. The radio receiving device measures the electric field levels of the respective channels by detecting the filtered signals using detectors 33a to 33c.
FIG. 4 is a block diagram showing another conventional radio receiving device disclosed in Japanese Unexamined Patent Publication No. SHO 63-177630. FIG. 3 shows the characteristics of a band-pass filter designed to filter a radio wave on an adjacent channel of lower frequency.
In addition to a frequency converter 31a for converting the frequency of a radio wave on a receiving channel into a lower-frequency, i.e., an IF, this radio receiving device includes other frequency converters 31b and 31c for converting the frequencies of radio waves on adjacent channels into lower-frequencies, i.e., IFs. The device measures the electric field levels of radio waves on the receiving and the adjacent channels by means of the band-pass filters 32a, 32b, and 32c.
Such a conventional radio receiving device includes not only a band-pass filter and detector for a receiving channel but also band-pass filters and detectors for adjacent channels, and it includes not only a frequency converter, a band-pass filter, and a detector for a receiving channel but also frequency converters, band-pass filters, and detectors for adjacent channels. Consequently, a number of electric components are required, resulting in a large-scale arrangement.